(1) Field of the Invention
The present invention relates to a process for the preparation of acrylic resin sheets having excellent heat moldability and solvent resistance.
(2) Description of the Related Art
Acrylic resin sheets are widely used in various fields because they have excellent transparency, gloss, surface hardness, mechanical strength, and heat resistance. However, conventional acrylic resin sheets have problems such that when placed in contact with an organic solvent such as ethanol or a paint thinner after heat molding, or subjected to FRP back-up processing with a polyester resin, crazing or cracking occurs and the usual excellent appearance thereof, a merit of acrylic resins, is degraded.
When a complicated molded article having a large elongation is prepared by vacuum-molding or compression-molding an acrylic resin sheet at a high temperature, the molding is limited by the flow characteristics of the molten polymer. For example, when preparing a molded article having corners and a concave face, a molded article having a drastically reduced sheet thickness at the corners (molded article having a nonuniform thickness) is obtained.
As a means for solving the former problem of cracking or crazing by a solvent, there is a method in which a polymer having a high molecular weight is used. But, if the molecular weight is high, the melt viscosity is also high, and thus the molding process becomes difficult.
As a means for solving the problem of poor moldability, there is a method in which a polymer having a low molecular weight is used, but if this method is adopted, the solvent resistance is degraded.
A complicated molded article can be obtained by heating a sheet at a high temperature, but according to this method, a molded article having a uniform thickness cannot be obtained and foaming or discoloration, sometimes appear in the sheet.
Accordingly, as apparent from the foregoing description, an acrylic resin sheet having an excellent moldability and solvent resistance has not been obtained by the prior art.